This invention relates generally to a support assembly for positioning read-write heads in a rotatable magnetic disc storage device and more particularly to a rotary actuator for positioning the read-write heads in a fixed disc drive.
Actuators for positioning read-write heads in rotatable magnetic disc drives are well known. Prior art disc drives typically employ either a linear actuator or a rotary actuator. Linear actuators employ a head support carriage that accesses the tracks on a magnetic storage disc radially. The head support carriage supports the read-write heads at one end and a voice coil motor at the other and rides or slides on cylindrical ways. The carriage is usually a complex die casting optimized for rigidity and low mass to produce a high bandwidth. However, the linear actuator does not lend itself to compact designs and is expensive to fabricate.
A rotary actuator typically comprises a pivoted lightweight bifurcated support arm having the read-write heads at one end and a voice coil motor at the other end. To achieve a compact design having a small drive enclosure the voice coil motor is usually placed near the pivot reducing the actuator lever arm. The rotary actuator therefore tends to suffer from poor mechanical advantage and requires a strong voice coil. Although compared to linear actuators rotary actuators are generally less expensive to fabricate, the motor force loads the pivot bearings requiring the use of expensive precision bearings for the pivot. Further, in use the actuator arm is in a bending mode resulting in increased settle time and a lower servo bandwidth. Inertia of the actuator system limits the speed at which the read-write heads can be moved reducing the head seek time.
U.S. Pat. No. 4,300,176 entitled "Fixed Disc Head Actuator Assembly" issued on Nov. 10, 1981 to Paul A. Gilovich and Joseph S. Tung discloses an actuator assembly for magnetic read-write heads having a pivot at one end of an actuator arm and the heads mounted on a head support extending from the actuator arm at the other end. A coil support and actuator means having a motor coil wound thereon extends from the side of the actuator arm opposite the head support and is positioned between the pivot and the head support. A pair of permanent magnets rigidly mounted to a chassis provide a gap in which the motor coil may move to cause the actuator arm to rotate about the pivot and move the read-write heads into cooperative relationship with one or more magnetic discs. The rotary actuator assembly disclosed by Gilovich et al. overcomes some of the disadvantages of earlier rotary actuators, but, because of the requirement of a coil support extension, does not achieve the compact design desirable in today's trend toward ever smaller disc drives.